The invention relates to the resolution of a mixture into at least a first fraction and a second fraction, these fractions differing from each other by their respective contents or compositions of at least one element or constituent, it being possible for the latter to be at least partially separated using any suitable separating technique employed during the resolution of the said mixture.
Many chemical engineering operations, such as distillation, liquid-liquid extraction, filtration or methodical washing of solids, require the presence of a counterflow or of a reflux. This counterflow, often indispensable to the operation, is generally obtained by gravity, using the difference in density of the separate phases, when such a difference exists and is large enough.
When the physical means capable of creating a reflux or a counterflow are absent or insufficient, as is the case with separations in a homogeneous phase or, in a heterogeneous phase, when the difference in density of the phases is not large enough, it becomes necessary to make use of other means.
Thus, in order to separate gas phases or fractions by gas diffusion, a reflux must be provided at each stage by extraction of a portion of the flows, followed by compression of that portion and its reinjection into the separating device.
Likewise, for operations involving at least one liquid phase or fraction and at least one solid phase or fraction, it is necessary to employ a succession of operations, such as filtration or centrifuging, removal of the cake, putting the latter back into suspension, pumping and, finally, reintroduction into the filtration.
The various means that should then be employed are often complex to run and expensive in terms of equipment and control means; they also involve considerable running and maintenance labor costs and a high energy cost. These means also have a negative impact on the reliability of the device for resolving the mixture or mixtures treated.
Document U.S. Pat. No. 2,609,277 relates to a column for liquid/liquid and gas/liquid contact, which may comprise porous or perforated walls, or else poppets, but not both. The passage of fluid from one stage to another is therefore controlled by the poppets, but there is no simultaneous enrichment or depletion operation.
In the pulsed apparatus described by document U.S. Pat. No. 4,133,714, intended for gas/solid/liquid exchanges, the stages are separated by a perforated wall which has an opening. However, no moveable shutter is employed. During the pulses, the liquid enters a stage freely and leaves a stage freely.
Document DE-A-25 02 371 describes conventional columns for pulsed liquid/liquid exchanges. The perforated walls separating the stages comprise openings or filters, but not both. The pistons employed never leave the corresponding cylinders, through the said cylinders.
Document SU-A-628,940 describes an apparatus for solid/liquid extraction. The pulsating stages are separated by perforated trays which partly retain the solids, without filters being involved.
The present invention aims to remedy all or some of these various drawbacks by combining the members or means providing and [sic] the separating functions with those providing the recycling or reflex functions.
By recycling, it should be understood to mean here any return of at least one flow towards or into a vessel for resolving a mixture, including the creation of a reflux or of a counterflow.
According to FIG. 1, a resolution process according to the invention makes it possible to resolve a mixture into at least a first fraction and a second fraction, these fractions differing from each other by their respective compositions of at least one element. This process comprises a plurality of elementary fractionation steps, in which steps at least two inflows, namely a first inflow (10) depleted in the first fraction and a second inflow (11) depleted in the second fraction are brought into contact with each other in order to obtain two outflows, namely a first outflow (12) enriched in the first fraction compared with the first inflow (10) and a second outflow (13) enriched in the second fraction compared with the second inflow (11), each elementary, non-stationary, fractionation step being carried out in an elementary fractionation stage (14), at which stage a mass-exchange buffer volume (15) is accumulated and each elementary fractionation step initiated and repeated periodically comprising at least the following phases:
a) depletion (4) in the first fraction, using a separating technique chosen from the group consisting of filtration, gas diffusion, ultrafiltration and reverse osmosis, of a first flow (16) relatively rich in the said first fraction, in order to obtain the first inflow (10),
b) introduction and mixing of the first inflow (10) in the buffer volume (15); then introduction and mixing of the second inflow (11) in the buffer volume (15),
c) extraction of the first outflow (12) from the buffer volume (15); then extraction of the second outflow (13) from the buffer volume,
the depletion (4) in the first fraction of the first flow being carried out concomitantly with the introduction of the first inflow (10),
the introduction of the first inflow (10) being carried out concomitantly with the extraction of the first outflow (12),
the introduction of the second inflow (11) being carried out concomitantly with the extraction of the second outflow (13),
the extraction of the second outflow (13) being interrupted, during the introduction of the first inflow (10), and the introduction of the first inflow (10) being interrupted during the extraction of the second outflow (13),
the introduction of the second inflow (11) being interrupted during the extraction of the first outflow (12), and the extraction of the first outflow (12) being interrupted during the introduction of the second inflow (11).